Reinforced blow-molded bumpers

ABSTRACT

The present invention provides a blow-molded vehicle part and a blow-molding process for generating a one-piece vehicle part with improved strength, aesthetic appearance and reduced weight and cost. The blow-molded vehicle part includes a front vehicle part portion and a back vehicle part portion, wherein the front vehicle part and the back vehicle part have at least an outer unreinforced layer of a thermoplastic that forms a smooth outer surface of the vehicle part and a reinforced inner layer.

This application is a 371 of PCT/US00/21621 Aug. 9, 2000 which claimsthe benefit of provisional application 60/148,889 filed Aug. 13, 1999.

BACKGROUND OF THE INVENTION

The present invention relates generally to processes for blow-moldingand to articles made by blow-molding. More particularly, the presentinvention relates to multi-layer blow-molded bumper structures thatincorporate reinforcing materials.

State-of-the-art automobile bumpers are typically manufactured bymolding thermoplastics using a variety of molding techniques. Thesetechniques strive to provide the best aesthetic qualities and structuralstrength, while reducing the material costs and weight of the finishedproduct. Many techniques and bumper structures utilize reinforcingmaterials, such as glass fibers in order to increase the structuralstrength and reduce weight. While the use of such reinforcing materialsis known to provide many desirable characteristics to molded articles,the use of such reinforcing materials in bumper structures produced byblow-molding techniques has heretofore been problematic. One reason forthis is that the use of reinforcing materials in blow-molded bumperstructures may produce irregularities or read-through in the outersurface finish of the bumper. Another reason is that the presence ofmany conventional reinforcing materials such as fiber reinforcement mayrender the bumper surface finish brittle and therefore unable to resistcracking when the bumper is subject to mild deformations.

In addition to the use of reinforcing materials, another known techniquefor increasing the strength of bumper structures involves the use oftacked-off bumper structures. In such structures, the internal surfacesof a bumper are made to contact and bond with each other to addstructural strength. Typically, however, tacked-off structures result ina thermal sink and read-through to the finished surface. As such, tackedoff structures have heretofore required the addition of a separatelymolded cover to provide an aesthetically pleasing exterior surface.

It would be desirable to provide blow-molded bumper structures whichaddresses the aforementioned shortcomings in the prior art.Specifically, it would be desirable to provide blow-molded bumperstructures that utilize reinforcing materials, such as glass, mineral orcarbon fibers or glass microspheres or nano-particles and which exhibitsuitable surface finishes, even in bumper structures that incorporatetacked-off structures.

SUMMARY OF THE INVENTION

The aforementioned problems are eliminated and the desired advantagesare realized by the present invention, which provides a blow-moldedbumper structure that incorporates one or more internal layers that arereinforced with reinforcing materials, such as glass, mineral or carbonfibers or glass microspheres or nano-particles. The reinforced layerincreases the strength of the bumper while reducing weight, density andmaterial costs. The reinforced layer also provides a thermal barrierthat acts to prevent read-through in tacked-off structures.

In one aspect, the invention may be defined as a blow-molded bumperincluding at least one inner layer containing a reinforcing material.More particularly, the invention may be defined as the aforementionedblow-molded bumper, wherein the reinforced layer is provided with glassfibers, mineral fibers, carbon fibers or glass microspheres ornano-particles.

In another aspect, the invention may be defined as a multi-layerblow-molded automobile bumper that includes at least one reinforcedlayer sandwiched between two unreinforced layers. More particularly, theinvention may be defined as the aforementioned bumper, wherein thereinforced layer is provided with glass fibers, ceramic microspheres,mineral fibers, carbon fibers or glass microspheres or nano-particles.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings which arc incorporated into and form a part ofthe specification, illustrate embodiments of the present invention and,together with the description, serve to explain the principles of theinvention. The drawings are only for the purpose of illustratingpreferred embodiments of the invention and are not to be construed aslimiting.

FIG. 1 is a cross-sectional view of a two-layered blow-molded automobilebumper including an inner reinforced layer;

FIG. 2 is a cross-sectional view of a three-layer blow-molded automobilebumper;

FIG. 3 is a cross-sectional view of a three-layer blow-molded automobilebumper; and

FIG. 4 is a cross-sectional view of a vehicle bumper manufactured inaccordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a cross-sectional view of a blow-molded automobile bumper 100according to a preferred embodiment of the present invention. Bumper 100includes a front portion 102 and back portion 104. An outer layer 106 isprovided as an unreinforced layer of thermoplastic which has desirableaesthetic qualities so as to form a smooth outer surface. Outer layer106 completely surrounds an inner layer 110, which is provided as areinforced thermoplastic. According to the invention, glass, mineral,carbon fibers, glass microspheres, ceramic microspheres ornano-particles may be used separately or in combination to provide thereinforcement to the reinforced inner layer 110. The glass may be in theform of glass fibers or glass microspheres. The mineral is typically inthe form of mineral fibers. The bumper 100 shown in FIG. 1 includes agap space 112 between the front portion 102 and a recessed portion 114,which is formed during the molding process. Clearly the method of thepresent invention may be used to manufacture, for example, a bumper, atail-gate, a door, or a running board.

As will be recognized by those of ordinary skill in the art, the bumper100 depicted in FIG. 1, may be manufactured by utilizing a multilayeredextrusion blow molding process. The first step is the extrusion of themultilayered thermoplastic parison to a length suitable for the size ofthe mold, wherein at least one inner layer includes at least one of:glass, mineral, carbon fibers, glass microspheres, ceramic microspheresor nano-particles. The parison is formed by heating thermoplasticmaterial to a temperature where it is very soft but still able to retainits shape. Second, the mold is closed around the parison. High pressuregas is injected into the parison expanding it against the inside of themold. Contact with the mold cools the material until hard. Finally themold is opened and the molded part is removed using appropriateequipment. This process is the same regardless of how many layers are inthe parison.

FIG. 2 illustrates a three-layer bumper 200 according to the invention.The bumper structure 200 includes a reinforced barrier layer 202 that issandwiched between an outer layer 204 and an inner layer 206. As in theexample of FIG. 1, reinforced barrier layer 202 may include glass,mineral, carbon fibers, glass microspheres, ceramic microspheres ornano-particles, for examples. This particular structure, with thereinforced barrier layer 202 sandwiched between two layers ofunreinforced material is useful to prevent the separation of layers upondeformation of the bumper structure.

FIG. 3 illustrates another three-layer bumper structure 300 according tothe invention. The bumper structure is like that shown in FIG. 2, exceptthat it includes a tacked-off portion 310 where an internal surface 312of the front portion 314 and an internal surface 316 of the recessedportion 318 are caused to bond together. Tack-off 310 between the frontportion 314 and back portion 340 can be controlled by designing thedistance in the specified area to be less than the thickness of theparison layers that line the mold.

As will be appreciated by those of ordinary skill in the art, thethermal insulating characteristics of the reinforced barrier layer 302,owing to the presence of glass, mineral, carbon fibers, glassmicropheres, ceramic microspheres or nano-particles, acts to preventread-through of the tacked-off portion to the outer surface 330 of thefront portion 314. Thus, the blow-molded bumper 300 may be formed in asingle step without the addition of an outer surface layer to concealread-through. Moreover, the tacked-off portion provides increasedstructural strength to the bumper 300.

The fiber-reinforced layer of the invention provides for reducedmaterial cost, since the fibers therein act as a relatively inexpensivefiller material to the relatively expensive thermoplastic materials.Thus, the fiber reinforced layer creates cost savings due to thedisplacement of comparatively heavy and costly resin materials withcomparatively inexpensive reinforcing materials or nano-particles. Theresult is a blow-molded, one-piece automobile bumper, with improvedstrength, aesthetic appearance and reduced weight and cost compared toprevious bumpers.

FIG. 4 is a cross-sectional view of a vehicle bumper 402 manufactured inaccordance with the present invention.

Although the preferred embodiments of the invention have been describedhereinabove in some detail, it should be appreciated that a variety ofembodiments will be readily available to persons utilizing the inventionfor a specific end use. The description of this invention is notintended to be limiting on this invention, but is merely illustrative ofthe preferred embodiment of this invention. Other products and methodsthat incorporate modifications or changes to that which has beendescribed herein are equally included within this application.Additional objects, features and advantages of the present inventionwill become apparent by referring to the above description of theinvention in connection with the accompanying drawings.

What is claimed is:
 1. A blow-molded vehicle part comprising: a frontvehicle part portion, and a back vehicle part portion, the front vehiclepart and the back vehicle part having an outer unreinforced layer of athermoplastic that forms a smooth outer surface of the vehicle part anda reinforced inner layer lying against the outer unreinforced layer thereinforced inner layer including at least one of: glass, mineral, carbonfibers, glass microspheres, ceramic microspheres and nano-particles, theback vehicle part portion including a recessed portion that is recessedtoward the front vehicle part portion to form a gap space between thefront vehicle part portion and the recessed portion, wherein therecessed portion with the gap space is formed during a molding process,the front vehicle part portion and the back vehicle part portion furtherincluding another layer of unreinforced thermoplastic that sandwichesthe reinforced inner layer between the outer unreinforced layer and saidother layer of unreinforced thermoplastic.
 2. The blow-molded vehiclepart of claim 1 wherein: the back vehicle part portion is recessedtoward the front vehicle part portion to form a distance between thefront vehicle part portion and the recessed portion that is less than athickness of parison layers that line the mold, bonding said other layerof unreinforced thermoplastic of the back vehicle part portion with saidlayer of unreinforced thermoplastic of the front vehicle part portionduring a molding process.
 3. The blow-molded vehicle part of claim 1wherein the vehicle is an automobile.
 4. The blow-molded vehicle part ofclaim 1 wherein the part is one of: a bumper, a tail-gate, a door, and arunning board.
 5. A blow-molding process for manufacturing amultilayered portion vehicle part comprising the steps of: extruding amultilayered thermoplastic parison to a length suitable for a size of apreselected mold, wherein at least one reinforced inner layer includesat least one of: glass, mineral, carbon fibers, glass microspheres,ceramic microspheres and nano-particles and wherein the reinforced innerlayer is sandwiched between an outer unreinforced layer and an innerunreinforced layer; closing the preselected mold around the parison;heating the parison to a temperature at which the parison is very softbut still able to retain a desired shape; injecting a high pressure gasinto the parison to expand the parison against an inside of thepreselected mold; and allowing the parison to-cool and, when thethermoplastic material has cooled sufficiently, removing the part fromthe preselected mold.
 6. The blow-molding process of claim 5 furtherincluding, before removing the part from the preselected mold, repeatingthe above steps at least one time using an unreinforced thermoplasticmaterial until a desired number of layers are formed.
 7. Theblow-molding process of claim 5 wherein the vehicle is an automobile. 8.The blow-molding process of claim 5 wherein the part is one of: abumper, a tail-gate, a door, and a running board.
 9. The blow-moldingprocess of claim 5 further including, before removing the part from thepreselected mold, repeating the above steps at least one time using areinforced thermoplastic material until a desired number of layers areformed.
 10. The blow-molding process of claim 5, the step of injecting ahigh pressure gas into the parison to expand the parison against aninside surface of the preselected mold a back vehicle part portion isrecessed toward a front vehicle part portion to form a distance betweenthe front vehicle part portion and the recessed portion that is lessthan a thickness of parison layers that line the mold, and the furtherstep of bonding an innermost layer of the back vehicle part portion withan innermost layer of the front vehicle part portion.